Solar irradiance at the top of the atmosphere on a plane normal to theincident¿radiation, and at the mean distance of the Earth from the Sun. Solarirradiance¿is also referred to as the solar constant. In satellite remotesensing, the¿solar irradiance is used as an onboard calibration of visible bandsensors.¿Some climate studies suggest that small variations in the solarirradiance¿associated with solar activity over days to decades may have aneffect the¿Earth's climate.¿The intensity of the sun's radiation at different wavelengths. The radiation isgenerally given in terms of solar constant \ S, defined in terms of flux oftotal radiation received outside the earth's atmosphere per unit area at meansun earth distance., and has the value S = 1.34 X 10*6 ergs cm*-2 sec*-1.